The present invention is directed to new and useful improvements in vacuum filters for separating solids from liquids and in particular to a horizontal tray filter that is provided with an elastic belt rotated in a longitudinal direction about spaced wheel members. The belt is provided with an endless row of trays fixed thereto which glide on a stationary vacuum channel formed in a horizontal filtration zone.
Horizontal tray vacuum filters are well known and with the horizontal arrangement of the filtration zone offer excellent filtration for many applications wherein the forming of the filter cake is supported by gravitation and wherein the cake washing can be carried out most efficiently. Certain horizontal filters are provided with a rotating disc or pans about the filter area which are separately divided pans which are tiltable for the cake discharge. There are other such machines known as reciprocating pan filters or intermittent belt filters which have the disadvantage of not being capable to carry out continuous filtration operation when the filter cloth is moved against the pan or vice versa and the vacuum is interrupted. The intermittent filtration which results limits the field of application for these filters especially if rapid filtering of slurry materials is desired. Furthermore the washing of the filter cake in these known machines is less efficient, complicated and difficult control systems are necessary for the operation of the filter.
In one such type filter shown in U.S. Pat. No. 1,862,050 to Donaldson a vacuum filter is shown wherein a pan filter is provided with trays that are rotatable on a conveyer with the filter cloth caulked into each single pan with a closed rim about the pan. In the latter type pan filter which is movable in a horizontal plane a number of separate pans are arranged like a conveyer with each pan having an individual connection to a lower vacuum filtrate channel whereby a gliding seal is effected between the pans and the vacuum channel. This type of filter has the disadvantage of being of a complex mechanical design. Further the cake cannot be discharged completely nor the filter cloth washed efficiently.
It is also already known in horizontal vacuum filters to provide an endless filter cloth over the filtration zone on the principle of a conveyer belt. These filters usually provide heavy endless rubber belts for example with a width of 1 m up to 6 m for supporting an endless filter cloth. The rubber belt is designed in such a way that it forms a gliding sealing with a vacuum filtrate channel in the filtration zone. These known rubber belt filters have the disadvantage of being heavy and difficult to handle and assemble and are extremely expensive. If the rubber belt is to be changed due to abrasion after a period of use this machine must be completely disassembled. Moreover, the applications for this kind of filter are limited as there are certain liquids in suspensions which may not be brought into contact with the rubber belt. It is possible, however, with these known rubber belt filters to lead the filter cloth by a belt onto the filter area at the inlet and outlet to the machine so that outside of the filtration zone washing devices are also available for the routine cleaning of the filter cloth. The disadvantage of these known rubber belt filters are the generally difficult assembly procedures, heavy weight of the massive rubber belt, and the considerable investment cost.
It is the object of the present invention to provide a novel horizontal pan or tray type vacuum belt wherein the filter cloth can be cleaned while the filter is in operation with a minimum of difficulty. To accomplish this objective an endless filter cloth is provided about the trays above the filtration zone and with the washing devices located outside the filtration zone and in a manner whereby each adjacent tray has a sealing engagement in the front and rear thereof with the next adjacent tray with each tray formed without rims so that the row of adjoining trays form one filter area. Further, all trays are linked with an elastic endless belt which is connected with the vacuum channel over openings with discharge of filtrate with the endless belt led in a gliding way on the vacuum channel. The trays supporting the endless filter belt are open on the two sides and fringeless whereby the assembled trays in a horizontal position form one single large filtration area. Each tray has its own connection with the vacuum channel underneath and is assembled in such a way that the tray and vacuum channel form together a gliding seal.
The above and other objects and advantages of the present invention will appear more fully hereinafter from a consideration of the detailed description which follows taken together with the accompanying drawings wherein one embodiment of the invention is illustrated.